This book was taught to children for over two millennia. But in the 1950s they decided that they don't want you to know what it teaches. It's the most successful textbook ever written and yet you never heard of it.
They removed it from schools because it teaches you how to think, and they figured out that a population of thinkers doesn't make for an efficient society. The Soviet Union had just sent the world's first satellite into orbit, Sputnik. The West feared lagging behind and getting nuked, and thought making the population unable to think is how you make Western society more competitive against the Soviet Union. They had drawn this lesson when Prussia lost a battle against Napoleon in 1806. Prussia determined it was because their soldiers were thinking too much as a result of having been taught logic.
https://en.wikipedia.org/wiki/Euclid%27s_Elements
To give you a taste of what it contains, the first thing you learn is how to draw a perfect like-sided triangle with a given length of the side, using only a compass and a straight edge, ie a ruler with no markings. Do you know how to do that? Then it tells you how you can know that the three sides are exactly the same length.
It's not like the math we are taught, which is a hollowed out version of math, this is the real thing, it gives you the actual foundation of math in deductive logic, working your way up from very basic concepts or observations, giving you a thorough comprehension of math, rather than rote memorization, and not just math but also logic, which is transferable to other areas of life, because it teaches you how to reason, how to think.
https://youtu.be/Q29U3_2PIiM
http://aleph0.clarku.edu/~djoyce/java/elements/bookI/propI1.html
https://farside.ph.utexas.edu/Books/Euclid/Elements.pdf (page 8)
https://www.c82.net/euclid/book1/#prop1
https://elements.ratherthanpaper.com/1.1
https://archive.org/details/elementsofeuclid00eucl/page/15
Euclid's Elements discussion